The present invention relates to a plasma process end point determination method and apparatus for determining an end point of a plasma process in a case where an etching process, etc. is performed by producing a plasma within a reaction chamber with use of either RF (radio-frequency) waves or microwaves or both.
The present invention also relates to a method and apparatus for evaluating the assembly reproducibility of a plasma process apparatus for carrying out an etching process, etc. by producing a plasma within a reaction chamber.
An emission spectroscopy method is widely adopted as one method of automatically determining the end of an etching or cleaning process on an object within a reaction chamber. In the emission spectroscopy method, an emission light intensity of a specific wavelength of plasma light, which is produced within the reaction chamber in accordance with the kind of etching gas, etc., is measured.
If a noise component is included in the light intensity of plasma light, it is removed by digital arithmetic operations in order to exactly determine the end point of etching or cleaning.
In an example of the method of determining the end of etching, with the noise component removed by digital arithmetic operations, a light intensity is digitally converted and sampled and a primary differential value of the sampling value is found from a moving average value of the sampling value. A secondary differential value of the sampling value is found from a difference in a moving average value of the primary differential value. A moving average value of the secondary differential value is compared with a preset value, whereby the end point of etching is determined.
However, in the method of determining the etching end point by using light intensity of the plasma, if a contamination lies on a plasma light take-in window provided at the reaction chamber, the contamination degrades transmissivity of plasma light and adversely affects the determination of the etching end point. In addition, flickering of plasma light due to instability of plasma adversely affects the determination of the etching end point.
Moreover, when an object of a novel material is etched, it is necessary to find a light intensity of plasma, which is enough to detect the etching end point, and a specific wavelength having a variation range.
Since the noise component is removed by finding moving averages twice or more, a time at which a signal variation occurs at the etching end point will delay after arithmetic operations, as compared to the state before the arithmetic operations. As a result, it becomes difficult to exactly determine the etching end point.
One example of the etching apparatus is a magnetron reactive ion etching (RIE) apparatus using a magnetron. In the magnetron RIE apparatus, the magnetron is rotated near the reaction chamber while RF power is supplied into the reaction chamber, and a plasma is produced within the reaction chamber to etch an object to be treated.
According to an etching end point determination method for this etching apparatus, a light intensity of plasma within the chamber is monitored through a light pass window, generally formed of quartz glass, and a variation point of the plasma light intensity is determined as an etching end point.
However, a variation point of plasma light intensity cannot be determined where the light pass window for monitoring plasma light intensity is contaminated or an area for etching is small due to a shift of a plasma caused by rotation of the magnetron, for example, where the area for etching is 10% or less of the entire area of an 8-inch semiconductor wafer, that is, the opening ratio is 10% or less.
In order to solve the above problems, an etching end point determination method has recently been adopted in which the plasma is regarded as part of a RF circuit and an impedance of the plasma is detected, and a variation point of the impedance is determined as etching end point.
However, in this method, too, the impedance varies at a rotational cycle of the magnetron due to fluctuations of the plasma caused by rotation of the magnetron. If the etching area is 10% or less as mentioned above, it is difficult to determine the etching end point because a variation of the etching end point is minute.
For example, FIG. 1 shows an RF voltage waveform detected by an RF circuit. The RF voltage waveform varies in accordance with the rotational cycle of the magnetron, and a minute variation of impedance at the etching end point cannot be recognized owing to noise at the rotational cycle of the magnetron. As a result, the etching end point cannot be determined.
As has been described above, the impedance varies at the rotational cycle of the magnetron due to fluctuations of plasma caused by the rotation of the magnetron, and if the process area is small, the process end point cannot be determined because the variation of the end of a plasma process such as an etching process is minute
In the plasma process apparatus, if objects are etched or ashed for a long time, products or products by reaction gas, which are produced by the etching or ashing, are deposited as films on the electrodes, parts constituting the electrodes and the inner wall surface of the reaction chamber. In addition, coating material on the electrodes and inner wall of the reaction chamber may be removed, and a uniform plasma process cannot be performed and come off deposit materials become particles. In order to solve these problems, the electrodes and reaction chamber are cleaned periodically and the electrodes and parts constituting the electrodes are exchanged periodically.
In order to clean the electrodes and reaction chamber and to exchange the electrodes and parts constituting the electrodes, the electrodes need to be disassembled and reassembled. In this case, if the states of the reassembled electrodes, etc. differ from the states before disassembly, a predetermined plasma process performance cannot be attained thereafter.
Under the circumstances, in the prior art, in order to evaluate the plasma process performance after the disassembly/reassembly of the electrodes, etc., a predetermined sample is subjected to the same plasma process as the actual one and the state of the processed sample is evaluated for adjustment.
However, in the method of subjecting the sample to the plasma process and evaluating the state of the processed sample for adjustment, since the state of the sample is evaluated, the evaluation method becomes an indirect one. Moreover, since the sample needs to be subjected to the same plasma process as the actual one, a long time is needed for the process.
In particular, if it is found from a sample evaluation result that a predetermined plasma process performance is not obtained, the plasma process performance of the sample has to be evaluated once again after the adjustment. This evaluation may be repeated until the predetermined plasma process performance is attained. Consequently, a longer time is needed, more samples are needed, and the cost increases.